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Bay Blog: shallow waters

Mar
28
2012

Chesapeake Bay underwater grasses decrease 21 percent in 2011

Fewer acres of bay grasses grew in the shallows of the Chesapeake Bay and its tidal rivers in 2011, according to scientists with the Chesapeake Bay Program. Bay grass acreage fell to an estimated 63,074 acres in 2011, down from 79,664 acres in 2010. This is the lowest Bay-wide acreage measured since 2006.

bay grasses on Susquehanna Flats

Because of heavy rainstorms that led to cloudy, muddy conditions that blocked monitoring efforts, only 57,956 acres of bay grasses were actually mapped in 2011. However, scientists believe about 5,119 acres of bay grasses may have been present during the height of the growing season, leading to the final estimated Bay-wide figure of 63,074 acres.

Bay grasses – also known as submerged aquatic vegetation or SAV – are a critical part of the Bay ecosystem. These underwater meadows provide fish, crabs and other aquatic life with food and habitat, absorb nutrients, trap sediment, reduce erosion, and add oxygen to the water. Bay grasses are also an excellent measure of the Bay's overall condition because their health is closely linked with the Bay’s health. 

“2011 was the year that bucked two trends we’ve seen over the last decade,” said Lee Karrh, chair of the Bay Program’s Submerged Aquatic Vegetation (SAV) Workgroup. “The Upper Bay had major decreases after years of increasing or sustained high acreages. On the other hand, the brackish parts of the Middle Bay witnessed dramatic increases in 2011, after prolonged decreases since the turn of the century.”

Experts agree that extreme weather conditions in 2010 and 2011 led to the substantial decrease in bay grasses. According to Bob Orth, scientist with the Virginia Institute of Marine Science (VIMS) and coordinator of the annual bay grass survey:

  • Summer 2010 was unusually hot, causing severe eelgrass die offs in the lower Bay. These beds had already been measured for the 2010 acreage survey, so these eelgrass losses were not officially recorded until 2011.
  • In spring 2011, heavy rains and resulting runoff created very muddy conditions in the upper Bay and its rivers during the bay grass growing season.
  • Last September, Hurricane Irene and Tropical Storm Lee brought even more rain and mud to the Bay’s waters.

In the upper Bay (from the mouth of the Susquehanna River to the Chesapeake Bay Bridge), bay grasses covered approximately 13,287 acres, down from 21,353 acres in 2010. This is most likely an underestimate because scientists did not monitor the area until November, once muddy conditions improved but well past the end of the growing season. One bright spot in the upper Bay was the more than doubling of bay grass acreage in the Chester River and near Eastern Neck.

In the middle Bay (from the Bay Bridge to Pocomoke Sound and the Potomac River), bay grasses decreased 4 percent to an estimated 34,142 acres, down from 35,446 acres in 2010. (Only 29,023 acres were mapped, but scientists estimate that an additional 5,119 acres may have been present.) Large eelgrass losses were observed in Tangier Sound. These were offset by widgeon grass gains in many areas, including Eastern Bay and the Choptank River.

In the lower Bay (south of Pocomoke Sound and the Potomac River), bay grasses covered 15,645 acres, down 32 percent from 22,685 acres in 2010. Hot summer temperatures in 2010 led to this significant drop in acreage, which offset any gains that followed in 2011. Eelgrass in many parts of the lower Bay had been recovering from similar heat-related losses that took place in 2005.

Despite Bay-wide losses, there were a few bits of good news for bay grasses last year. The huge, dense bed on the Susquehanna Flats – which has increased threefold in size over the past 20 years – survived the late summer tropical storms, showing how resilient healthy bay grass beds can be to natural disturbances. Also, scientists recorded the first-ever bay grass bed in the mainstem James River since the area was first surveyed in 1998.

Annual bay grass acreage is estimated through an aerial survey, which is conducted from late spring to early autumn. Residents can do their part to help restore bay grasses by not fertilizing in the spring and planting more plants to reduce polluted runoff from backyards.

For detailed information about 2011 bay grasses acreage, including aerial photos and year-to-year comparisons, visit VIMS' SAV blog. For more information about the aerial survey and bay grass monitoring efforts, visit VIMS’ SAV website.



Aug
27
2010

What habitats are found in the Chesapeake Bay watershed?

There are several different kinds of habitats found in the Bay’s watershed. Each one is important to the survival of the watershed’s diverse wildlife. Habitats also play important roles in Bay restoration.

Chesapeake Bay habitats include:

  • Forests
  • Wetlands
  • Streams and rivers
  • Shallow waters
  • Tidal marshes
  • Aquatic reefs
  • Open waters

Forests

Forests covered approximately 95 percent of the Bay’s 64,000-square-mile watershed when Europeans arrived in the 17th century. Now, forests only cover about 58 percent of the watershed.

Forests are important because they provide vital habitat for wildlife. Forests also filter pollution, keeping nearby waterways cleaner. Forests act as huge natural sponges that absorb and slowly release excess stormwater runoff, which often contains harmful pollutants. Forests also absorb airborne nitrogen that might otherwise pollute our land and water.

Wetlands

A typical Bay wetland.

Wetlands are transitional areas between land and water. There are two general categories of wetlands in the Chesapeake Bay watershed: tidal and non-tidal. Tidal wetlands, found along the Bay's shores, are filled with salt or brackish water when the tide rises. Non-tidal wetlands contain fresh water

Just like forests, wetlands act as important buffers, absorbing and slowing the flow of polluted runoff to the Bay and its tributaries.

Streams and rivers

Streams and rivers not only provide the Chesapeake Bay with its fresh water, they also provide many aquatic species with critical habitat. Fish, invertebrates, amphibians and other wildlife species all depend on the Bay’s tributaries for survival.

When the Bay’s streams and rivers are in poor health, so is the Bay, and the great array of wildlife it harbors is put in danger.

Shallow waters

Shallow waters are the areas of water from the shoreline to about 10 feet deep. Shallow waters are constantly changing with the tides and weather throughout the year. The shallows support plant life, fish, birds and shellfish.

Tidal marshes 

Tidal marshes in the Bay's shallows connect shorelines to forests and wetlands. Marshes and provide food and shelter for the wildlife that lives in the Bay's shallow waters. Freshwater marshes are found in the upper Bay, brackish marshes in the middle Bay and salt marshes in the lower Bay.

Aquatic reefs

Aquatic reefs are solid three-dimensional habitats made up of densely packed oysters. The reefs form when oyster larvae attach to larger oysters at the bottom of the Bay.

Reefs provide habitat and communities for many aquatic species in the Bay, including fish and crabs. The high concentration of oysters in aquatic reefs improve water quality by filtering algae and pollutants from the water.

Open waters 

Open waters are beyond the shoreline and the shallows. Aquatic reefs replace underwater bay grasses, which cannot grow where the sunlight cannot penetrate deep waters. Open water provides vital habitat for pelagic fish, birds and invertebrates.

Each of these habitats are vital to the survival of the Chesapeake Bay’s many different species of wildlife. It's important to protect and restore habitats to help promote the overall health of the Bay. So do your part to save the Bay by protecting habitats near you – find out how.

Do you have a question about the Chesapeake Bay? Ask us and we might choose your question for the next Question of the Week! You can also ask us a question via Twitter by sending a reply to @chesbayprogram! Be sure to follow us there for all the latest in Bay news and events



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